The present invention relates to a photolithography, and more particularly, to a phase shift mask for double patterning and a method for exposing a wafer using the same.
As semiconductor devices are highly integrated, it is more and more difficult to form a fine pattern due to a resolution limit in a photolithography process. That is to say, although a size of the pattern required in the semiconductor device becomes finer and finer, a photolithography technology cannot keep up with the trend that the size of the pattern becomes finer.
In order to overcome such resolution limit in the exposure, there has been suggested Double Patterning Technology (DPT) using two masks. The DPT is a method that divides the entire pattern which should be included in one mask into two masks and transfers the entire pattern through two-time photolithography process using respective masks. Since this exposure using the DPT performs two-time photolithography process using two masks, registration of the mask in an exposure apparatus is a very important factor. In other words, the patterns respectively disposed in the two masks can be transferred onto a wafer with accurate distance only when the two masks in which the pattern is divisionally disposed are registered at exactly the same position in the exposure apparatus. However, it is not easy to perform accurately such mask registration. Also, when the registration error is more than a certain level, a distance between the pattern transferred through a first mask and the pattern transferred through a second mask is excessively narrowed or broaden, which may result in pattern defects.